Immersible diver{3 s microphone

ABSTRACT

This application discloses an invention including a ceramic gradient microphone insensitive to mask cavity acoustics, essentially flat in pressure response to 10,000 Hz for use in deep submergence helium atmospheres, and capable of withstanding compression, decompression and intermittent flooding. In essence, there is provided a microphone having a diaphragm mounted to a bimorph ring and includes a unique construction to provide improved frequency response and gradient characteristics, plus drainage characteristics.

Morrow et al.

[ lMMERSlBLE DIVERS MICROPHONE [75] Inventors: Charles T. Morrow, Arlington;

Austin J. Brouns, Dallas. both of Tex.

[73] Assignec: The United States of America as represented by the Secretary of the Navy, Washington. DC.

{221 Filed: Dec. 27, l97l 1211 Appl. No; 212,002

[52] U.S. Cl 179/] UW; 179/1155 ES [51] Int. Cl. H04R 15/00; H04R 7/12 158] Field of Search 179/1 UW. 115.5 ES. 110 A: 340/10 [56] References Cited UNITED STATES PATENTS 2.607.858 3/1952 Mason 340/10 1 1 Sept. 30, 1975 2.910.545 10/1959 Glenn 179/110 A 3.439.128 4/1969 Sobel ct a] 179/1 [0 A 3.660.809 5/1972 Pearson 340/10 Primary L.\umiuer-Douglas W. Olms Allmney. Agent. or FirmRv S. Sciascia; R. E. ONcill 5 7 1 ABSTRACT 6 Claims, 2 Drawing Figures US. Patent Sept. 30,1975 3,909,529

FIG. 2 IO FIG. I 25 O O A Z 4 A 0 0 0 0 0 z .4 33 v OOOQO l2 1| 7 7 E 2 20 z A- ;'Z9 34 Z Z A 27 4 122 A a INVENTORS CHARLES T. MORROW AUSTIN J.BROUNS Z4 Z3 5 ATTORNEY IMMERSIBLE DIVERS MICROPHONE Deep submergence microphones usable with helium atmospheres are required by divers operating under increased pressure conditions. Using helium, an inert gas, instead of nitrogen, has the advantage that bubbles will not develop in the blood stream of the diver which cause bends and the other problems associated with dissolved nitrogen in the blood stream. Many microphones have been tried in the environmental conditions of a diving mask. Among those are magnetic microphones which require close clearances between moving parts. When a mask is flooded, sea water penetrates into these spaces, causing corrosion and, in time, an accumulation of salt crystals. Setting the first mechanical element of the diaphragm and piezoelectric ceramic bimorph ring to approximately 20,000Hz provides smooth response in the speech range, extending to l0,000Hz or higher in helium-oxygen atmospheres, without any need for acoustic compensation for the resonance. Such compensation would be altered and degraded by changes in atmospheric pressure and composition. The relatively low sensitivity associated with the 20,000Hz resonance is made up for by solid state amplifier circuitry.

With the construction provided by this invention, there are no moving parts requiring close clearances. The protective coverplates are not only perforated but are separated from the housing sufficiently to form one-tenth inch, self-draining slots at their peripheries. The perforations toward the divers lips may be cleared by blowing. If any water remains temporarily in the perforation on the far side, there is only a minor deterioration of performance.

A pressure gradient microphone placed in a divers helmet close to the lips is insensitive to the acoustics of the diving mask cavity. The diaphragm of a gradient microphone is open to sound on both sides and responds to a pressure difference. The term noisecancelling microphone is frequently used, as the sensitivity is greater for the approximately spherical waves emerging from the lips than for the more nearly plane waves characteristic of ambient noise.

It is an objective of this invention to provide an improved immersible diver's microphone capable of rapid drainage and immune to deterioration of performance due to deposit of salt crystals.

It is still a further objective of this invention to provide an improved gradient microphone utilizing spherical diaphragm coupled to a bimorph ring affixed to a housing and mounted in a central cavity therein and having perforated end plates including peripheral slots and a plurality of small circular openings.

Therefore, it is an objective of this invention to pro- 1 vide an improved immersible divers microphone comprising, a housing member having a hollow central portion and having first and second ends, a ceramic bimorph member disposed in the hollow portion, an epoxy affixing the ring within the housing, the ring being substantially normal to the longitudinal axis of the housing, a diaphragm affixed to the ring, first and second end plates affixed to the housing individually having leg members positioning the end plates at distance from the housing member for providing drainage from the central portion, electrical connecting means attached to the bimorph ring and a preamplifier circuit coupled to the electrical connecting means for connecting electrical signals generated by the ring.

Yet a further objective of this invention is to provide an improved gradient microphone with protective end plates mounted 0.l inch from the housing to allow for rapid drainage due to flooding.

Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conj unction with the accompanying drawings wherein:

FIG. 1 is a front view of one embodiment of the invention and FIG. 2 is a cross sectional view along lines AA in FIG. 1.

FIG. 1 wherein the immersible microphone is designated generally as has an electrical connection 11 coupled to microphone 10. A solid state circuit can be mounted in the expanded part 12 or in the housing, part 15, but does not form a part of this invention and is not shown.

The microphone itself, consists of a housing member 15 having extending therethru along longitudinal axis 16, a hollow central portion 17. Disposed along the axis 16 is a ceramic bimorph ring 18 of a three sandwich layer construction. A kapton diaphragm 20 is affixed to an inner edge of the ring 18 and has electrical connections 24 and 23 connected thereto for conducting an electrical signal to an external circuit not shown. Ring 18 is affixed to housing 15 by an epoxy compound 25 that also holds a support ring 26.

The support ring 26 has a recessed portion 27 designed to receive legs 28 and 29 of cover plate 30. Housing 15 also has a recessed portion 32 designed to receive support legs 33 and 34 of a second cover plate 35. Each cover plate is affixed to the housing 15 thru screws, two of which 40 and 41 are shown in FIG. I. The cover plate and individually include a plurality of holes designed as 45 for the purpose of allowing the sound waves to reach the microphones central portion.

The cover plates are individually spaced approximately the same distance from the housing to provide for drainage in the event the microphone is flooded.

In one successful embodiment of the invention the gradient microphone was tested in atmospheres of 97.5 percent helium at a simulated depth of 650 feet. Listening tests and Sonagrams showed no difference in the helium speech due to any effect of mask cavity as opposed to the open boom mount. Comparisons of Sonagrams for helium speech with those for sea level speech showed a simple proportional upward shift of formant frequencies (resonance frequencies of the vocal tract) of approximately 2.9. There was no indication of the nonlinear shift (first formants more than the second) frequently reported in the literature as a result of the pressures of deep submergence.

One of the initial problems overcome by this design was that of helium penetration from extreme depth and potential decomposition from decompression and salt water immersion. In the construction of the microphone the potting compound was degassed in a vacuum before using, and filling operations included several evacuations and recompressions to help avoid trapping any gas.

Experiments showed that water would drain readily under its own weight thru a slit less than one tenth of an inch in width, therefore, the protective cover plate for the diaphragm may be separated from the microphone body this tenth of an inch for successful operation. However, coating the inside of the cover plates with a water repellent may permit the slots to be less than one tenth of an inch and still let water drain off without difficulty. The one tenth of an inch is not a critical dimension but is an optimum design parameter One successful form of epoxy used was Minnesota Mining and Manufacturing Scotch-cast resin No. 8 with a trace of Plastic Molders Supply PMS No. 4640 black dye.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

I claim:

1. An improved lmmersible Microphone designed for coupling to external circuitry for reproduction of sound comprising:

a. a housing member having a hollow central portion,

said hollow portion having first and second ends;

b. a ceramic bimorph ring disposed in said hollow portion;

c. an epoxy compound affixing said ring within said housing;

d. a diaphragm shaped as a small segment of a sphere affixed to said ring;

e. first and second end plates affixcd to said housing individually having leg members positioning said end plates a distance from said housing members for providing drainage from said hollow central portion;

and

f. electrical connecting means attached to said bimorph ring for connecting electrical signals generated by said ring to said external circuitry.

2. An Improved lmmersible Microphone of claim I wherein said housing member has a longitudinal axis along said hollow central portion and said central portion has a cylindrical shape about said axis.

3. An Improved lmmersible Microphone of claim 2 wherein the bimorph ring is substantially circular and normal to said axis.

4. An Improved lmmersible Microphone of claim 3 wherein said first and second end plates are normal to said axis.

5. An Improved lmmersible Microphone of claim 4 wherein said end plates are spaced about one tenth of an inch from said housing.

6. An Improved immersible Microphone of claim 5 wherein said end plates are treated with a water repellent material for increased drainage. 

1. An improved Immersible Microphone designed for coupling to external circuitry for reproduction of sound comprising: a. a housing member having a hollow central portion, said hollow portion having first and second ends; b. a ceramic bimorph ring disposed in said hollow portion; c. an epoxy compound affixing said ring within said housing; d. a diaphragm shaped as a small segment of a sphere affixed to said ring; e. first and second end plates affixed to said housing individually having leg members positioning said end plates a distance from said housing members for providing drainage from said hollow central portion; and f. electrical connecting means attached to said bimorph ring for connecting electrical signals generated by said ring to said external circuitry.
 2. An Improved Immersible Microphone of claim I wherein said housing member has a longitudinal axis along said hollow central portion and said central portion has a cylindrical shape about said axis.
 3. An Improved Immersible Microphone of claim 2 wherein the bimorph ring is substantially circular and normal to said axis.
 4. An Improved Immersible Microphone of claim 3 wherein said first and second end plates are normal to said axis.
 5. An Improved Immersible Microphone of claim 4 wherein said end plates are spaced about one tenth of an inch from said housing.
 6. An Improved Immersible Microphone of claim 5 wherein said end plates are treated with a water repellent material for increased drainage. 